Production of a semiconductor device involves a step of forming an electroconductive film on the surface of a wafer to form a wiring layer by photolithography, etching etc., a step of forming an interlaminar insulating film on the wiring layer, etc., and an uneven surface made of an electroconductive material such as metal and an insulating material is generated on the surface of a wafer by these steps. In recent years, processing for fine wiring and multilayer wiring is advancing for the purpose of higher integration of semiconductor integrated circuits, and accordingly techniques of planarizing an uneven surface of a wafer have become important.
As the method of planarizing an uneven surface of a wafer, a CMP method is generally used. CMP is a technique wherein while the surface of a wafer to be polished is pressed against a polishing surface of a polishing pad, the surface of the wafer is polished with slurry having abrasive grains dispersed therein. As shown in FIG. 1, a polishing apparatus used generally in CMP is provided for example with a polishing platen 2 for supporting a polishing pad 1, a supporting stand (polishing head) 5 for supporting a polished material (wafer) 4, a backing material for uniformly pressurizing a wafer, and a mechanism of feeding an abrasive. The polishing pad 1 is fitted with the polishing platen 2 for example via a double-sided tape. The polishing platen 2 and the supporting stand 5 are provided with rotating shafts 6 and 7 respectively and are arranged such that the polishing pad 1 and the polished material 4, both of which are supported by them, are opposed to each other. The supporting stand 5 is provided with a pressurizing mechanism for pushing the polished material 4 against the polishing pad 1.
Patent Document 1 proposes a method for polishing a semiconductor substrate, comprising fixing a semiconductor substrate to a polishing head; pushing a polishing layer having a micro-rubber A hardness of 70 degrees or more, which is fixed to a polishing platen with a cushion layer interposed therebetween having a volume modulus of 600 kg/cm2 or more and a compression elastic modulus of 10 kg/cm2 or more and 140 kg/cm2 or less, against the semiconductor substrate; and rotating the polishing head or the polishing platen or both of them in the state where the warps or irregularities of the semiconductor substrate itself are absorbed into the cushion layer, so that the semiconductor substrate is polished.
Recently, a polishing pad has also been increased in size with upsizing of semiconductor wafers, and thus work of bonding a large polishing pad to a polishing platen has become difficult. In the work of bonding a polishing pad to a polishing platen, it is necessary to bond the polishing pad as flatly as possible to the polishing platen. However, if the polishing pad becomes larger in size, air becomes easy to enter between the polishing pad and the polishing platen during bonding process. Since the portion where the air enters projects convexly, there was the problem that defects (e.g., deterioration in polishing uniformity, tear of polishing layer caused by dresser, etc.) due to such a portion could occur in the polishing process of the semiconductor wafer.